/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import com.google.common.annotations.GwtCompatible;
import java.lang.ref.WeakReference;
import java.util.Iterator;
import java.util.Locale;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.regex.Pattern;
import javax.annotation.Nullable;

/**
 * Methods factored out so that they can be emulated differently in GWT.
 *
 * @author Jesse Wilson
 */
@GwtCompatible(emulated = true)
final class Platform {
    private static final Logger logger = Logger.getLogger(Platform.class.getName());
    private static final PatternCompiler patternCompiler = loadPatternCompiler();

    private Platform() {}

    /** Calls {@link System#nanoTime()}. */
    static long systemNanoTime() {
        return System.nanoTime();
    }

    static CharMatcher precomputeCharMatcher(CharMatcher matcher) {
        return matcher.precomputedInternal();
    }

    static <T extends Enum<T>> Optional<T> getEnumIfPresent(Class<T> enumClass, String value) {
        WeakReference<? extends Enum<?>> ref = Enums.getEnumConstants(enumClass).get(value);
        return ref == null ? Optional.<T>absent() : Optional.of(enumClass.cast(ref.get()));
    }

    static String formatCompact4Digits(double value) {
        return String.format(Locale.ROOT, "%.4g", value);
    }

    static boolean stringIsNullOrEmpty(@Nullable String string) {
        return string == null || string.isEmpty();
    }

    static CommonPattern compilePattern(String pattern) {
        Preconditions.checkNotNull(pattern);
        return patternCompiler.compile(pattern);
    }

    static boolean usingJdkPatternCompiler() {
        return patternCompiler instanceof JdkPatternCompiler;
    }

    private static PatternCompiler loadPatternCompiler() {
        ServiceLoader<PatternCompiler> loader = ServiceLoader.load(PatternCompiler.class);
        // Returns the first PatternCompiler that loads successfully.
        try {
            for (Iterator<PatternCompiler> it = loader.iterator(); it.hasNext();) {
                try {
                    return it.next();
                } catch (ServiceConfigurationError e) {
                    logPatternCompilerError(e);
                }
            }
        } catch (ServiceConfigurationError e) { // from hasNext()
            logPatternCompilerError(e);
        }
        // Fall back to the JDK regex library.
        return new JdkPatternCompiler();
    }

    private static void logPatternCompilerError(ServiceConfigurationError e) {
        logger.log(Level.WARNING, "Error loading regex compiler, falling back to next option", e);
    }

    private static final class JdkPatternCompiler implements PatternCompiler {
        @Override
        public CommonPattern compile(String pattern) {
            return new JdkPattern(Pattern.compile(pattern));
        }
    }
}
